CHARACTERIZATION OF HUMAN CREATINE-KINASE BB AND MB ISOFORMS BY MEANSOF ISOELECTRIC-FOCUSING

Isoforms of creatine kinase (creatine-N-phosphotransferase, CK, EC 2.7 .3.2), BE and MB, were isolated from healthy human brain tissue and ca rdiac muscle, respectively, and were characterized by means of isoelec tric focusing (IEF), CK-BB isoforms in Tris-HCl buffer were focused at pI 4.5 (a tissue form) and those in fresh sera from healthy adults we re focused at pI 5.0, 5.1 and 5.2 (plasma forms). The IEF patterns of CK-BB isoforms were not altered following treatment with carboxypeptid ase B and incubation in fresh serum at 37 degrees C; thus, it was foun d that there was no lysine at the C-terminal of the CK-B subunit and C K-BB isoforms were not results of the removal of lysine. Three CK-BB i soforms in fresh sera were identified to be oxidized, intermediate and reduced forms from the anodal side, respectively, by treatment with h ydrogen peroxide and 2-mercaptoethanol. The oxidized form of CK-BB see med to have higher affinity to IgG than the other two plasma forms of CK-BB. On the other hand, CK-MB isoforms in Tris-HCl buffer were focus ed at pI 5.4 (a tissue form) with a minor band at pI 5.2 and those in sera were focused at pI 5.0, 5.1, 5.2 (plasma forms) and 5.4. Four CK- MB isoforms were identified to be reduced, intermediate and oxidized f orms without lysine from the anodal side, respectively, and the cathod al band was a tissue form with lysine.